In telecommunications, a femtocell—originally known as an Access Point Base Station—is a small cellular base station, typically designed for use in residential or small business environments. It connects to the service provider's network via broadband (such as DSL or cable). A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. The femtocell incorporates the functionality of a typical base station, but extends it to allow a simpler, self-contained deployment.
A Node B is an element of a 3G macro Radio Access Network (RAN), and a 3G Home Node B (3G HNB) is the 3GPP's term for a 3G femtocell. Within a 3G HNB Access Network there are two network elements: a 3G HNB (or femtocell) and a 3G Home Node B Gateway (3G HNB GW). The 3G HNB is connected to an existing residential broadband service and provides 3G radio coverage for 3G handsets within a home. The 3G HNB GW is installed within an operator's network and aggregates traffic from a large number of 3G HNBs back into an existing core service network.
The 3G network, as well as the next generation standard, referred to as Long Term Evolution (LTE), is an Internet Protocol (IP)-based network architecture. As the telecommunications network has evolved, mobile devices have also evolved to act as IP devices. IP devices typically implement IP Multimedia Subsystem (IMS) sessions that utilize packet-switched (PS) communications instead of CS communications. Legacy CS devices, however, are unable to communicate with the PS network, and hence, the legacy CS devices are unable to utilize services or take advantage of the capabilities offered by IMS systems or other PS networks. Furthermore, multi-mode (e.g., 2G/3G multi-mode devices) devices may initially connect via PS communications, but roam to an area that is not serviced by PS communications. In these situations, there is a need for a method and system that allow the legacy CS devices to utilize IMS services when communicating via a femtocell, as well as allow multi-mode devices to roam between PS networks and CS networks.